1. Field of the Invention
Embodiments of the present invention generally relate to temperature compensated oscillators and, more specifically, to dynamic temperature compensation for a digitally controlled oscillator using dual MEMS resonators.
2. Description of the Related Art
Many electronic devices include timing circuitry that usually runs continuously so that accurate time and date information, among other things, may always be maintained. Oscillators are commonly used in the timing circuitry of such devices to produce the required timing signal. However, with many mechanical oscillators, the resonant frequency of the signal produced by the oscillator depends upon temperature. Consequently, oscillator circuits usually require some sort of temperature compensation functionality.
A typical temperature compensation system includes a temperature sensor configured to detect temperature changes at regular intervals and a frequency compensation circuit configured to correct the output frequency of the oscillator every time a temperature change is detected. Electronic temperature sensors that provide either digital values indicative of the absolute temperature of the oscillator or values indicative of relative changes in temperature are often used in such temperature compensation systems. One example of an electronic temperature sensor includes an analog temperature measurement device coupled with an analog-to-digital converter (ADC). The temperature measurement device generates an analog voltage signal based on the temperatures measured from the oscillator. The ADC receives analog temperature values from the temperature measurement device at a certain rate, converts the analog values to digital form, and then averages the digital values to obtain a final digital representation of the measured temperature.
One major drawback to using this type of temperature compensation system is that obtaining digital temperature measurements with a precision better than 1 degree Centigrade (° C.) from an electronic temperature sensor requires complex and expensive circuits that consume relatively large amounts of power. In addition, if the temperature fluctuates rapidly between sampling intervals, large errors in the output frequency can result. One solution to this problem is to decrease the time interval between temperature measurements. However, fast and precise electronic temperature sensing circuits are even more complex and expensive to implement, consume even more power, and may not be available for particular applications.
As the foregoing illustrates, what is needed in the art is a temperature compensation system that addresses one or more of the problems set forth above.